Introduction: Both the portion size and energy density of foods have large effects on energy intake, and contribute to the obesity epidemic. Nutritional education for children is generally based on the food-pyramid concept and the “5 (fruit and vegetable) a day” approach. The ED concept is applied successfully in the nutritional education of adults but for children it is not clear how well they can understand and apply it. Methods: A motion-controlled serious game for children addressing all the three core areas of nutrition, physical activity, and psychosocial factors has been developed (KOP-Kids Obesity Prevention Program). It is the first serious game, which extensively targets the ED concept in the nutrition section. After the introduction of the ED concept the children analyze various foods in the different food groups with regards to their contents of fat, carbohydrates, protein, fiber and water. In the next step, the children have to apply their knowledge in two different tasks. These tasks allow us to measure not only whether the children have understood the ED concept but also whether they can apply it to unknown foods under time pressure. Results: Eighty-three school children with a mean age of 9.7±0.5 years and mean BMI z-score of 0.1±1.2 played the game. The children were able to understand the ED concept and were able to classify unknown foods equally as the known foods according to their ED. However, it took the children longer to categorize the unknown foods versus the known foods. Discussion: Primary school children do understand the ED concept and the latter could be applied in standard nutritional education for children.